Methods for the synthesis of chemical compounds

ABSTRACT

Methods for synthesis of chemical compounds by catalytic transfer hydrogenation comprise forming a mixture of a starting material, a hydrogen donor material and a catalyst. The catalyst is selected from a catalytic form of carbon, a polyethylene glycol phase transfer agent, and mixtures thereof. The mixture is heated at a temperature of from 30° to 400° C. in the presence of at least one alkali or alkaline earth metal compound to cause reduction of the starting material by catalytic transfer hydrogenation and form the desired chemical compound product.

This application is a division of application Ser. No. 08/191,504 filedFeb. 4, 1994 U.S. Pat. No. 5,478,548.

FIELD OF THE INVENTION

The present invention relates to methods for the synthesis of chemicalcompounds using catalytic transfer hydrogenation. More specifically, thepresent invention relates to methods for the synthesis of chemicalcompounds by catalytic transfer hydrogenation of a starting material inthe presence of a hydrogen donor material, a catalyst and at least onealkali or alkaline earth metal compound.

BACKGROUND OF THE INVENTION

Hydrogenation of unsaturated carbon structures using hydrogen gas and ametal catalyst is a reaction well known to the chemical industry.However, the use of molecular hydrogen poses a serious risk of fire orexplosion, with subsequent formation of toxic by-products.

Reduction reactions which employ an organic molecule that functions asthe hydrogen donor in the presence of a catalyst are also known in theart and commonly referred to as catalytic transfer hydrogenationmethods. The catalytic transfer hydrogenation reaction may begeneralized as follows: ##STR1## In principle, the donor compound can beany organic compound whose oxidation potential is sufficiently low thathydrogen transfer can occur under relatively mild conditions. Forexample, at temperatures greater than about 300° C., benzene serves as ahydrogen acceptor and can be reduced to cyclohexane.

Conventional catalytic transfer hydrogenation methods have shown onlylittle commercial potential, generally owing to poor yields and longreaction times, and as a result of the very successful exploitation ofthe aforementioned methods employing molecular hydrogen with metalliccatalysts and hydrides. Cortese et al, J. Org. Chem., 43, 3985 (1978),have disclosed the reductive elimination of halogens from a number ofhalogenated compounds employing triethylammonium halogens, a temperatureof 100° C., triethylammonium formate as a hydrogen donor, a reactiontime of 6 hours and a palladium catalyst. While some dehalogenation wasachieved, the reaction was incomplete.

Bamfield et al, Synthesis, 537 (1978), have disclosed the use of anaqueous alkaline sodium formate solution, a palladium catalyst, asurfactant, a 32 percent hydroxide solution and a temperature of 95° C.to remove halogens from compounds in the synthesis of symmetricalbiphenyl. The disclosed reaction resulted in only moderate yields ofbiphenyl. Wiener et al, J. Org. Chem., 50, 21 (1991) have describedmethods for catalytic transfer hydrogenation of aryl halides forproducing the corresponding arenes. A palladium catalyst effected thetransfer hydrogenolysis of the aryl halides using potassium and sodiumformate as the hydrogen donor at a temperature of 60° C. and in thepresence of an initial amount of water.

In other studies, Crawford et al, Trans. Faraday Soc., 58, 2452 (1962),demonstrated the reduction of alkynes to cis-alkenes by employingmolecular hydrogen and palladium catalyst, and Wiener et al havereported on the application of aqueous formate salts as hydrogen donors,Int. J. Hydrogen Energy, 14, pp 365-370 (1989).

Most of the elements that have proved to be valuable catalysts forcatalytic transfer reductions ate a part of the second transition seriesin the periodic table. Salts and complexes of Pd, Pt, Ru, Ir, Rh, Fe,Ni, and Co, and particularly of palladium, have all been used primarilyas heterogeneous catalysts. The most active catalysts reported forheterogeneous transfer reduction are based on palladium metal. However,the transition series metal catalysts employed in typical catalytictransfer hydrogenation reactions are costly, and new technology must bedeveloped and implemented for their recovery. Strenuous efforts havebeen undertaken to find catalysts from less expensive metals for use incatalytic hydrogen transfer reduction reactions.

Thus, if catalytic transfer hydrogenation methods are to be effectivefor the synthesis of chemical compounds, they must be able to employ lowcost hydrogen donors and low cost, non-toxic catalysts which do notrequire extensive recovery treatment. Additionally, the methods mustreduce synthesis time as compared with existing catalytic transferhydrogenation processes, and they must produce high yields of thedesired products. It would also be advantageous for such methods to beeffected in pressurized, closed and non-pressurized reaction systems.Thus, a need exists for improved catalytic transfer hydrogenationprocesses for producing chemical compounds.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to providecatalytic transfer hydrogenation methods for synthesizing chemicalcompounds. It is a further object of the present invention to providecatalytic transfer hydrogenation methods for synthesizing chemicalcompounds, wherein the methods employ low cost hydrogen donors and lowcost, non-toxic catalysts which do not require extensive recoverytreatment. It is a further object of the present invention to providecatalytic transfer hydrogenation methods which require reduced synthesistime and provide increased yields of the desired chemical compoundproducts, particularly as compared with prior catalytic transferhydrogenation processes. It is also an object of the present inventionto provide catalytic transfer hydrogenation methods which may beeffected in pressurized, closed and non-pressurized reaction systems.

These objects are achieved by various embodiments of the presentinvention. Specifically, the present invention relates to methods forthe synthesis of chemical compounds by catalytic transfer hydrogenation.The methods comprise providing a mixture of a starting material, ahydrogen donor material and a catalyst selected from a catalytic form ofcarbon, a polyethylene glycol phase transfer agent, and mixturesthereof, and heating the mixture at a temperature of from 30° to 400° C.in the presence of at least one alkali or alkaline earth metal compoundto cause reduction of the starting material by catalytic transferhydrogenation and form the desired chemical compound products. It hasbeen discovered that the combination of a hydrogen donor material and acatalyst selected from a catalytic form of carbon, a polyethylene glycolphase transfer agent, and mixtures thereof, in combination with heatingin the presence of at least one alkali or alkaline earth metal compoundcauses catalytic transfer hydrogenation reduction of a starting materialunder relatively mild conditions and forms desired chemical compoundproducts in high yields. The present methods are advantageous inavoiding the use of the metal catalysts which are employed inconventional catalytic transfer hydrogenation reduction reactions andwhich are costly and difficult to recover.

These and additional objects and advantages provided by the presentinvention will be further understood in view of the following detaileddescription.

DETAILED DESCRIPTION

The methods according to the present invention are directed to thesynthesis of a chemical compound by catalytic transfer hydrogenation ofa starting material. A mixture of the starting material, a hydrogendonor material and a catalyst selected from a catalytic form of carbon,a polyethylene glycol phase transfer agent and mixtures thereof areheated in the presence of at least one alkali or alkaline earth metalcompound. Temperatures of from 30° to about 400° C. are employed in theheating step. The starting material is reduced by a catalytic transferhydrogenation reaction and one or more desired chemical compoundproducts are produced.

The starting material which is employed in the methods of the presentinvention may be either an organic or inorganic material. The particularselection of a suitable starting material will of course depend on thechemical compound which is to be produced. As will be described infurther detail below, nitrogen-containing materials may be employed asstarting materials for the production of amines and/or ammonia. Coal,oil, shale, heavy oil, polymers and other fossil fuel precursors andproducts may be employed as starting materials, particularly in theproduction of gases, including ammonia, hydrogen sulfide and lightaliphatic compounds, aromatic hydrocarbons, phenols, aryl amines andheterocyclic compounds. In other embodiments of the present methods, thestarting material may comprise a metal containing compound such as ahydroxide, carbonate or sulfonate and may be used to produce productssuch as metal oxides, hydrides, carbides or sulfides. In anotherembodiment of the present methods, the starting material may comprise ahalogenated aliphatic compound and the chemical compound which isproduced by the catalytic transfer hydrogenation reaction may compriseeither a halogenated or non-halogenated product. A particularlypreferred example employing a halogenated aliphatic compound as astarting material is a method for the catalytic transfer hydrogenationof ethylene dichloride, wherein vinyl chloride monomer is the resultantproduct.

The hydrogen donor material which is employed in the methods of thepresent invention provides hydrogen ions for the reduction reaction ofthe starting material effected by the catalytic transfer hydrogenationmechanism. The hydrogen donor compound may comprise any hydrogen bearingmaterial under the appropriate reaction conditions. Example of suitablehydrogen donor materials include crude and waste oil, polymers, wasteplastics and coal, organic compounds, hydrogen gas and the like.Preferred hydrogen donor compounds include high boiling polar ornonpolar solvents, including fatty acids, aliphatic alcohols orhydrocarbons, amines and the like. In one embodiment, the hydrogen donormaterial may be modified to effect easier release of the hydrogen ions,whereby the methods of the invention may be conducted at lowertemperatures. For example, the hydrogen donor material may be treatedwith an alkylating agent which can produce tertiary hydrogen atoms inthe modified hydrogen donor compound. The tertiary hydrogen atoms aremore easily releasable to form hydrogen ions, whereby the methods may beconducted at lower temperatures. The hydrogen material is employed in anamount sufficient to provide the molar amount of hydrogen ions necessaryfor the desired reduction of the starting material.

In order to activate the hydrogen donor material to produce free radicalhydrogen atoms, a catalyst is employed. In accordance with an importantfeature of the present invention, the catalyst is selected from acatalytic form of carbon, a polyethylene glycol phase transfer agent,and mixtures thereof. One example of a carbon source which is watersoluble and suitable for use in the present methods comprises acarbohydrate, for example sucrose. Another example of a carbon sourcesuitable for use in the present methods comprises carbon black, or othercarbon source having a relatively large surface area. In the alternateembodiment wherein the catalyst comprises a polyethylene glycol phasecatalyst, the polyethylene glycol may be of a molecular weight selectedfrom a wide range, i.e. from about 50 to 20,000 Daltons or more. Apreferred polyethylene glycol phase catalyst comprises tetraethyleneglycol. In a further embodiment, the catalyst comprises a combination ofa carbon source and a polyethylene glycol phase catalyst. The catalystis employed in the present methods in an amount sufficient to activaterelease of hydrogen from the donor material and effect the desiredhydrogenation reduction reaction to form the chemical compound product.

The mixture of the starting material, hydrogen donor material andcatalyst is heated at a temperature from 30° to 400° C. in the presenceof at least one alkali or alkaline earth metal compound. The alkali oralkaline earth metal compound may comprise, for example, a carbonate,bicarbonate, oxide or hydroxide, or a compound which generates acarbonate, bicarbonate, oxide or hydroxide. The alkali or alkaline earthmetal compound may be employed in the mixture in an aqueous solution orin a high boiling solvent. Alternatively, the alkali or alkaline earthmetal compound may be included in the form of a solid dispersion orsuspension. If the alkali or alkaline earth compound is added in a highboiling solvent, suitable solvents have a boiling point of at least 100°C., and more preferably from about 200° to about 500° C. Preferredsolvents include hydrocarbon compounds. In an additional embodiment, thealkali or alkaline earth metal compound may be employed in an aqueoussolution, wherein the aqueous solution further contains a high boilingsolvent.

The alkali or alkaline earth metal compound, for example, a carbonate,bicarbonate, oxide or hydroxide, is employed in a molar ratio of fromabout 1:1 to about 10:1, with respect to the starting material. Thespecific amount of alkali or alkaline earth metal compound which isrequired is dependent on the specific starting material and desiredproduct. Any of the alkali and alkaline earth metals, or mixturesthereof, may be employed in the methods of the invention. Preferredalkali metals include lithium, sodium and potassium, with sodium andpotassium being particularly preferred.

The alkali and alkaline earth metal carbonates, bicarbonates and oxidesmay be preferred for use in certain systems owing to their lower toxiceffects as compared with alkali and alkaline earth metal hydroxides.However, the hydroxide and oxide compounds are preferred for use insystems where the starting material is acidic in nature or comprises ahydrocarbon material.

In one embodiment, an alkali metal compound is used in combination withan alkaline earth compound. More particularly, the alkali metalcompounds are preferred to initiate the catalytic transfer hydrogenationreduction reaction. However, alkali metal compounds are generally moreexpensive than alkali earth metal compounds. Accordingly, the alkalineearth metal compounds, for example alkaline earth metal oxides, may beused in combination with the alkali metal compound to providestoichiometric amounts of cations for reaction with the anions liberatedfrom the starting material. When the alkali metal compound and thealkaline earth metal compound are used in combination, the alkalineearth metal compound also absorbs indigenous and chemically formed waterin the reaction mixture. Accordingly, less of the more costly alkalimetal compound may be used in combination with an alkaline earth metalcompound to effect the chemical compound synthesis at a lower cost forraw materials.

As is demonstrated in Example 2 hereafter, an alkali or alkaline earthmetal compound may also be used as the starting material in the presentmethods.

The heating step which is employed in the present methods may beconducted at a temperature between 30° and about 400° C. depending onthe starting material and hydrogen donor materials employed, and thedesired chemical compound product. In some embodiments, a temperature inthe range of from about 50° to about 150° C. is preferred while in otherembodiments, a temperature in the range of from about 300° to about 350°is preferred. In still another embodiment, a relatively low temperaturein the range of up to about 40° C. is preferred. The examples set forthherein provide additional teachings which will assist one of ordinaryskill in the art in selecting the appropriate temperature range to beemployed with particular starting materials, and hydrogen donormaterials. The heating may be provided by an external heat source, or byinitiation of an exothermic reaction.

Depending on the composition of the starting material, the hydrogendonor material and the catalyst, the mixtures which are employed in thepresent invention may be in the form of an aqueous solution, an organicsolvent solution or a solid dispersion or suspension.

The following examples are presented in order to further demonstratespecific embodiments of the invention. Throughout the presentspecification and examples, parts and percentages are by weight, unlessotherwise indicated.

EXAMPLE 1

This example demonstrates the production of amines and ammonia using thecatalytic transfer hydrogenation methods of the present invention.Ammonia is synthesized based on the following reaction:

    N.sub.2 (g)+3H.sub.2 →2NH.sub.3

This reaction is highly exothermic and consequently production plantsmust be carefully designed to control temperatures. Conventionalprocesses are conducted at 100 to 1000 atmospheres and require hightemperatures in excess of 500° C. Such processes convert only 5 to 20percent of the synthesis gases (N₂ /H₂). Iron catalysts are widely usedin conventional ammonia synthesis. However, these catalysts loose theiractivity when heated to temperatures above 520° C. and are deactivatedwhen in contact with phosphorus, arsenic, sulfur and other contaminants.Thus, in the conventional processes, the synthesis gases must bepurified before the ammonia synthesis commences to prevent the catalystsfrom becoming deactivated.

The process according to the present invention may be used to produceammonia from a nitrogen bearing material and a hydrogen donor atrelatively lower pressures of from 1 to 50 atmospheres. Anynitrogen-containing materials or compounds, including crude deposits ofinorganic compounds of nitrogen, may be employed as a starting materialin this process. Additionally, numerous hydrogen bearing materials,including crude and waste oils, polymers, waste plastics and coal, canbe used as the hydrogen donor material. The catalyst, either a catalyticform of carbon or a polyethylene glycol phase catalyst, or a mixturethereof, is not poisoned or deactivated by high temperatures. Aminecompounds may be synthesized according to the same synthesis schemeexcept that the reaction temperature is controlled, and a base andvarious solvents including water are introduced into the reaction mediumto control the degree of reduction and therefore prevent the amines frombeing further reduced to ammonia.

In this example, dinitrobenzene is reduced to amine compounds andammonia. Specifically, a mixture of 100 ml of a hydrocarbon solvent, 20ml of water, 9.0 g of 2,4-dinitrobenzene, 5.0 g sodium hydroxide and 1.0g phase catalyst, carbon catalyst mixture was formed. The hydrocarbonsolvent served as the hydrogen donor material. The mixture was agitatedby stirring and heated to 50° to 100° C. for 15 to 30 minutes to effectcomplete reduction of the nitro groups to amines. Heating at highertemperature and/or a longer heating period of the mixture resulted infurther reduction of the amine groups to ammonia.

EXAMPLE 2

This example demonstrates the synthesis of an inorganic compound usingthe catalytic transfer hydrogenation methods of the present invention.In conventional processes, hydrogen is reacted with sodium attemperatures between 200° and 350° C. to produce sodium hydrides.However, hydrogen gas in the presence of metallic sodium poses a greatrisk of fire and/or explosion. Additionally, at temperatures of from300° to 385° C., sodium and sodium hydroxide react to produce sodiumoxide and hydrides. Sodium monoxide substantially free of sodium andsodium hydroxide is produced by sweeping the reaction zone with an inertgas to remove hydrogen. The present invention offers an alternativemethod for the production of compounds such as sodium oxide and sodiumhydride.

A mixture comprising 40 grams of sodium hydroxide (corrected formoisture), 100 ml aliphatic hydrocarbon solvent, and 1.0 g catalyst wasformed and placed in a 200 ml round bottom flask. The flask was equippedwith a stirring condenser and a receiver to collect water. The contentsof the flask were heated to 300° to 350° C. for 1 hour, after which thewater in the receiver was measured and compared to that produced in asimilar process which did not employ the catalyst or hydrogen donor. Themeasured water of 18 g produced from the reaction according to thepresent invention demonstrated that sodium hydroxide had been reduced tothe sodium hydride. The example demonstrates the use of the alkali metalcompound as the starting material.

A similar method may be used to prepare other metal hydrides, includingpotassium, rubidium and cesium hydrides, as well as the alkaline earthmetal hydrides at and above the temperature employed for the sodiumhydride synthesis disclosed above. These methods may also be employed toreduce calcium carbonate, sulfate and other forms of inorganic compoundsto carbides, sulfides or oxides using temperatures significantly lowerthan those employed in conventional methods for the production of suchcompounds.

EXAMPLE 3

In the past, coal has been subjected hydrogenolysis to obtain coalchemicals including gases, hydrocarbons, phenols, aryl amines andheterocyclic compounds. Generally, these processes have employed 300 to400 percent excess hydrogen gas, temperatures of 840° to 1000° F. andpressures of 4,000 to 6,000 psi to yield higher value aromatics andother byproducts.

In accordance with the methods of the present invention, variouschemical compounds, including liquid fuels, may be obtained from coal,oil, shale, heavy oil, polymers, plastics and other fossil fuelprecursors and products. As an example, a mixture of 100 ml high boilingpoint aliphatic oil and 50 g crushed coal (20-30 mesh) was formed. Thehigh boiling point aliphatic oil served as a hydrogen donor material andprovided a reaction medium. The oil had a boiling point range of 327° to410° C. The mixture was placed in a 200 ml round bottom flask equippedwith a stirrer and 5.0 g sodium hydroxide and 1 g catalyst (polyethyleneglycol phase transfer catalyst, carbon catalyst or a mixture thereof)were added. The flask was equipped with a fractionating column and areceiver. The contents of the flask were heated to 350° C. for two hoursafter which the contents of the flask and receiver were sampled.Products identified from the catalytic transfer hydrogenation reactionsof the coal included ammonia, hydrogen sulfide and light aliphaticgases, aromatic hydrocarbons, phenols, aryl amines and heterocycliccompounds. Additionally, greater than 50% of the solid treated coal wasliquified.

EXAMPLE 4

This example demonstrates the synthesis of chemical compounds fromhalogenated aliphatics, which compounds may serve as chemicalintermediates in the preparation of polymers and the like. Thesynthesized compounds may be partially dehalogenated or fullydehalogenated. An example of a partially dehalogenated compound preparedaccording to the present methods is vinyl chloride prepared fromethylene dichloride, while an example of a fully dehalogenated compoundprepared according to the present methods is ethylene prepared fromethylene dichloride. These reactions are as follows:

Partial dehalogenation: ##STR2## Full dehalogenation: ##STR3##

In conventional processes, vinyl chloride monomer is synthesized fromethylene dichloride by thermal dehydrochlorination using a temperatureof 500° to 550° C. and a pressure of about 24 atmospheres. The methodsof the present invention provide an alternate method for preparing vinylchloride monomer. Specifically, a mixture of 50 ml hydrocarbon solvent(boiling point range of 100° to 200° C.), 50 g sodium hydroxide, 20 gethylene dichloride and 1 g polyethylene phase transfer catalyst wasformed. The mixture was placed in a 200 ml round bottom flask equippedwith a stirrer, a condenser with receiver and a gas collector. Thereaction was initiated by the addition of 5-10 ml water or by heating to30° to 40° C. with stirring in different reaction runs. The 20conversion of ethylene dichloride to vinyl chloride monomer occurredrapidly with temperature control in a continuous process. It will beapparent that this method is a significant improvement over the priorart method described above.

Ethylene, propylene and other unsaturated chemical intermediates wereprepared from partially dechlorinated compounds such as vinyl chloridemonomer. The partially dechlorinated starting material was combined in aone liter pressure vessel with 200 ml hydrocarbon, 10 g sodium hydroxideand 1 g of carbon catalyst. The vessel was closed and heated withstirring to a temperature of 280° to 330° C. for one to four hours.After cooling, the contents of the vessel were analyzed and it wasdetermined that only ethylene was present. Similar experiments havedemonstrated the synthesis of unsaturated, dehalogenated monomers fromhalogenated aliphatics for use in various chemical processes.

The preceding examples are set forth to illustrate specific embodimentsof the invention and are not intended to limit the scope of the methodsof the present invention. Additional embodiments and advantages withinthe scope of the claimed invention will be apparent to one of ordinaryskill in the art.

What is claimed is:
 1. A method for the synthesis of a chemical compoundselected from the group consisting of hydrocarbons, phenols, arylamines,heterocyclics, ammonia and hydrogen sulfide by catalytic transferhydrogenation, comprising (a) providing a mixture of a polymericstarting material, a hydrogen donor material, and a catalyst selectedfrom the group consisting of a catalytic form of carbon, a polyethyleneglycol phase transfer agent, and mixtures thereof; and (b) heating themixture at a temperature of from 30° to 400° C. in the presence of atleast one alkali or alkaline earth metal compound to cause reduction ofthe starting material by catalytic transfer hydrogenation and form thechemical compound.
 2. A method as defined by claim 1, wherein thehydrogen donor material is selected from the group consisting of organiccompounds, polymers and hydrogen gas.
 3. A method as defined by claim 1,wherein the hydrogen donor material is selected from the groupconsisting of fatty acids, aliphatic alcohols, aliphatic hydrocarbonsand amines.
 4. A method as defined by claim 1, wherein the catalystcomprises a catalytic form of carbon.
 5. A method as defined by claim 1,wherein the catalytic form of carbon comprises a carbohydrate or carbonblack.
 6. A method as defined by claim 1, wherein the catalyst comprisesa polyethylene glycol phase transfer agent.
 7. A method as defined byclaim 1, wherein the catalyst comprises a mixture of a catalytic form ofcarbon and a polyethylene glycol phase transfer agent.
 8. A method asdefined by claim 1, wherein the at least one alkali or alkaline earthmetal compound is selected from the group consisting of carbonates,bicarbonates, oxides, hydroxides and compounds which generatecarbonates, bicarbonates, oxides or hydroxides.
 9. A method as definedby claim 1, wherein the heating step is conducted at a temperature inthe range of from about 50° to about 150° C.
 10. A method as defined byclaim 1, wherein the heating step is conducted at a temperature in therange of from about 300° to about 350° C.
 11. A method as defined byclaim 1, wherein the heating step is conducted at a temperature in therange of up to about 40° C.